It is generally accepted in the bio-pharmaceutical arts, that improving the stability of an immunogenic composition (e.g., a protein immunogen, a polysaccharide-protein conjugate) is a necessary and highly desirable goal. For example, an immunogenic composition must appear fresh, elegant and professional when administered to a patient. Any changes in stability and/or physical appearance of the immunogenic composition, such as color change, clouding or haziness, may cause a patient or consumer to lose confidence in the product. Furthermore, because many immunogenic formulations are dispensed in multiple-dose containers, uniformity of dose content of the active ingredient (e.g., a polysaccharide-protein conjugate) over time must be assured (e.g., a cloudy solution can lead to a non-uniform dosage pattern). Additionally, the immunogenic composition must be active throughout its “expected” shelf life, wherein any breakdown of the immunogenic composition to an inactive or otherwise undesired form (e.g., an aggregate) lowers the total concentration of the product.
Several reports in the literature have suggested that the stability of a particular immunogenic composition (e.g., a protein immunogen, a polysaccharide-protein conjugate) is at least in part dependent upon the specific protein or carrier protein (Ho et al., 2001; Ho et al., 2002; Bolgiano et al., 2001). For example, stability analysis of meningococcal C (MenC) polysaccharides and Haemophilus influenzae type b (Hib) polysaccharides, conjugated to either a tetanus toxoid (TT) or a CRM197 carrier protein, revealed different stability profiles dependent on the carrier protein (Ho et al., 2002). In another study (Ho et al., 2001), MenC-CRM197 conjugates from two different manufacturers were analyzed (Ho et al., 2001), wherein the MenC-CRM197 conjugates differed in their conjugation chemistry and length of conjugate polysaccharide (both having the same carrier protein, CRM197). Data from this study further indicated that factors such as conjugation chemistry (e.g., reductive amination either directly or via a chemical spacer group), number of conjugation sites, polysaccharide chain length, pH, storage buffer, storage temperature(s) and freeze/thaw cycles also influence the stability of an immunogenic composition.
Thus, when developing a formulation for an immunogenic composition, many factors must be considered to ensure a safe, stable, robust and cost effective product. Such considerations include, but are not limited to, chemical stability of the immunogenic composition (e.g., hydrolysis of saccharides, de-polymerization of polysaccharides, proteolysis or fragmentation of proteins), physical/thermal stability of the immunogenic composition (e.g., aggregation, precipitation, adsorption), compatibility of the immunogenic composition with the container/closure system, interactions between immunogenic composition and inactive ingredients (e.g., buffers, salts, excipients, cryoprotectants), the manufacturing process, the dosage form (e.g., lyophilized, liquid), the environmental conditions encountered during shipping, storage and handling (e.g., temperature, humidity, shear forces), and the length of time between manufacture and usage.
It has been suggested in the art, that silicone oil, which induces protein secondary and tertiary conformational changes, might be responsible for the aggregation/precipitation seen in certain protein pharmaceutical preparations (Jones et al., 2005). For example, several reports in the 1980s implicated the release of silicone oil from disposable plastic syringes as the causative agent in the aggregation of human insulin (Chantelau and Berger, 1985; Chantelau et al., 1986; Chantelau, 1989; Bernstein, 1987; Baldwin, 1988; Collier and Dawson, 1985). Chantelau et al. (1986) observed that after three or more withdrawals from a ten-dose preparation of insulin (using a siliconized disposable syringe), the vial would begin clouding due silicone oil contamination, thereby resulting in aggregation and deactivation of the insulin (Chantelau et al., 1986). Paradoxically, silicone oil is a necessary component of plastic syringes, as it serves to lubricate the rubber plunger and facilitate transfer of the plunger down the syringe barrel (i.e., silicone oil improves the syringeability of the formulation).
Furthermore, the use of silicone oil is not limited to syringes, as it is used as a coating for glass vials to minimize protein adsorption, as a lubricant to prevent conglomeration of rubber stoppers during filing procedures, as a lubricant critical to the processability/machinability of glass and elastomeric closures and as a lubricant to ease needle penetration of vial rubber stoppers. Additionally, the siliconization of syringes, glass vials, rubber stoppers and the like, is not a well controlled nor standardized process, and as such, there is a high degree of variability of the silicone oil content from one lot to another.
There is therefore an ongoing need in the art for formulations which enhance stability and inhibit precipitation of immunogenic compositions.